libstdc++-v3/doc/html/manual/support.html

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   2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 4.  Support</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.78.1" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="std_contents.html" title="Part II.  Standard Contents" /><link rel="prev" href="std_contents.html" title="Part II.  Standard Contents" /><link rel="next" href="dynamic_memory.html" title="Dynamic Memory" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 4.
   3   Support
   4
   5 </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="std_contents.html">Prev</a> </td><th width="60%" align="center">Part II.
   6     Standard Contents
   7   </th><td width="20%" align="right"> <a accesskey="n" href="dynamic_memory.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="std.support"></a>Chapter 4.
   8   Support
   9   <a id="id-1.3.4.2.1.1.1" class="indexterm"></a>
  10 </h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="section"><a href="support.html#std.support.types">Types</a></span></dt><dd><dl><dt><span class="section"><a href="support.html#std.support.types.fundamental">Fundamental Types</a></span></dt><dt><span class="section"><a href="support.html#std.support.types.numeric_limits">Numeric Properties</a></span></dt><dt><span class="section"><a href="support.html#std.support.types.null">NULL</a></span></dt></dl></dd><dt><span class="section"><a href="dynamic_memory.html">Dynamic Memory</a></span></dt><dt><span class="section"><a href="termination.html">Termination</a></span></dt><dd><dl><dt><span class="section"><a href="termination.html#support.termination.handlers">Termination Handlers</a></span></dt><dt><span class="section"><a href="termination.html#support.termination.verbose">Verbose Terminate Handler</a></span></dt></dl></dd></dl></div><p>
  11     This part deals with the functions called and objects created
  12     automatically during the course of a program's existence.
  13   </p><p>
  14     While we can't reproduce the contents of the Standard here (you
  15     need to get your own copy from your nation's member body; see our
  16     homepage for help), we can mention a couple of changes in what
  17     kind of support a C++ program gets from the Standard Library.
  18   </p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="std.support.types"></a>Types</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="std.support.types.fundamental"></a>Fundamental Types</h3></div></div></div><p>
  19       C++ has the following builtin types:
  20     </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
  21         char
  22       </p></li><li class="listitem"><p>
  23         signed char
  24       </p></li><li class="listitem"><p>
  25         unsigned char
  26       </p></li><li class="listitem"><p>
  27         signed short
  28       </p></li><li class="listitem"><p>
  29         signed int
  30       </p></li><li class="listitem"><p>
  31         signed long
  32       </p></li><li class="listitem"><p>
  33         unsigned short
  34       </p></li><li class="listitem"><p>
  35         unsigned int
  36       </p></li><li class="listitem"><p>
  37         unsigned long
  38       </p></li><li class="listitem"><p>
  39         bool
  40       </p></li><li class="listitem"><p>
  41         wchar_t
  42       </p></li><li class="listitem"><p>
  43         float
  44       </p></li><li class="listitem"><p>
  45         double
  46       </p></li><li class="listitem"><p>
  47         long double
  48       </p></li></ul></div><p>
  49       These fundamental types are always available, without having to
  50       include a header file. These types are exactly the same in
  51       either C++ or in C.
  52     </p><p>
  53       Specializing parts of the library on these types is prohibited:
  54       instead, use a POD.
  55     </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="std.support.types.numeric_limits"></a>Numeric Properties</h3></div></div></div><p>
  56     The header <code class="filename">limits</code> defines
  57     traits classes to give access to various implementation
  58     defined-aspects of the fundamental types. The traits classes --
  59     fourteen in total -- are all specializations of the template class
  60     <code class="classname">numeric_limits</code>, documented <a class="link" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00593.html" target="_top">here</a>
  61     and defined as follows:
  62     </p><pre class="programlisting">
  63    template&lt;typename T&gt;
  64      struct class
  65      {
  66        static const bool is_specialized;
  67        static T max() throw();
  68        static T min() throw();
  69
  70        static const int digits;
  71        static const int digits10;
  72        static const bool is_signed;
  73        static const bool is_integer;
  74        static const bool is_exact;
  75        static const int radix;
  76        static T epsilon() throw();
  77        static T round_error() throw();
  78
  79        static const int min_exponent;
  80        static const int min_exponent10;
  81        static const int max_exponent;
  82        static const int max_exponent10;
  83
  84        static const bool has_infinity;
  85        static const bool has_quiet_NaN;
  86        static const bool has_signaling_NaN;
  87        static const float_denorm_style has_denorm;
  88        static const bool has_denorm_loss;
  89        static T infinity() throw();
  90        static T quiet_NaN() throw();
  91        static T denorm_min() throw();
  92
  93        static const bool is_iec559;
  94        static const bool is_bounded;
  95        static const bool is_modulo;
  96
  97        static const bool traps;
  98        static const bool tinyness_before;
  99        static const float_round_style round_style;
 100      };
 101    </pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="std.support.types.null"></a>NULL</h3></div></div></div><p>
 102      The only change that might affect people is the type of
 103      <code class="constant">NULL</code>: while it is required to be a macro,
 104      the definition of that macro is <span class="emphasis"><em>not</em></span> allowed
 105      to be <code class="constant">(void*)0</code>, which is often used in C.
 106     </p><p>
 107      For <span class="command"><strong>g++</strong></span>, <code class="constant">NULL</code> is
 108      <code class="code">#define</code>'d to be
 109      <code class="constant">__null</code>, a magic keyword extension of
 110      <span class="command"><strong>g++</strong></span>.
 111     </p><p>
 112      The biggest problem of #defining <code class="constant">NULL</code> to be
 113      something like <span class="quote">“<span class="quote">0L</span>”</span> is that the compiler will view
 114      that as a long integer before it views it as a pointer, so
 115      overloading won't do what you expect. (This is why
 116      <span class="command"><strong>g++</strong></span> has a magic extension, so that
 117      <code class="constant">NULL</code> is always a pointer.)
 118     </p><p>In his book <a class="link" href="http://www.aristeia.com/books.html" target="_top"><span class="emphasis"><em>Effective
 119       C++</em></span></a>, Scott Meyers points out that the best way
 120     to solve this problem is to not overload on pointer-vs-integer
 121     types to begin with.  He also offers a way to make your own magic
 122     <code class="constant">NULL</code> that will match pointers before it
 123     matches integers.
 124     </p><p>See the
 125       <a class="link" href="http://www.aristeia.com/books.html" target="_top"><span class="emphasis"><em>Effective
 126       C++ CD</em></span></a> example.
 127     </p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="std_contents.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="std_contents.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="dynamic_memory.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Part II.
 128     Standard Contents
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